Light measurement device and light measurement method

ABSTRACT

A spectrometry device includes a light source, an integrator configured to have an internal space in which a long afterglow emission material is disposed and output detection light from the internal space, a spectroscopic detector, an analysis unit configured to analyze a photoluminescence quantum yield of the long afterglow emission material, and a control unit configured to control switching between presence and absence of input of excitation light to the internal space and an exposure time in the spectroscopic detector. The control unit controls the light source so that the input of the excitation light to the internal space is maintained in a first period and the input of the excitation light to the internal space is stopped in a second period, and controls the spectroscopic detector so that an exposure time in the second period becomes longer than an exposure time in the first period.

TECHNICAL FIELD

The present disclosure relates to a light measurement device and a lightmeasurement method.

BACKGROUND ART

As an object to be measured by a spectrometry device, a long afterglowemission material such as a luminescent material or a phosphorescentmaterial has attracted attention. Such a long afterglow emissionmaterial is, for example, a material that accumulates sunlight orexcitation light of a fluorescent lamp or the like, and sustains lightemission for a constant period of time even after radiation of theexcitation light is stopped. In recent years, Non-Patent Literature 1has reported the world's first organic luminescent material that doesnot contain rare-earth elements. This organic luminescent materialrealizes an emission lifetime of an hour or more under room temperatureconditions by the mixing of two kinds of organic materials. In view ofsuch circumstances, applied research of a long afterglow emissionmaterial in various fields such as safety displays, guidance signs,clock faces, lifesaving equipment, interior design, or cell imaging isexpected to progress increasingly actively in the future.

CITATION LIST Non-Patent Literature

[Non-Patent Literature 1] Nature, 2017, doi:10. 1038/nature 24010, R.Kabe and C. Adachi

SUMMARY OF INVENTION Technical Problem

One evaluation item of a light-emitting material includes aphotoluminescence quantum yield. The photoluminescence quantum yield isa value indicating the light emission efficiency of a light-emittingmaterial. The photoluminescence quantum yield is calculated by dividingthe number of photons emitted from a light-emitting material by thenumber of photons absorbed into the light-emitting material. However,there is a problem in that the intensity of light emission in theabove-described long afterglow emission material is extremely weakerthan the intensity of excitation light, and that the intensity of lightemission after the radiation of the excitation light is stoppedfluctuates over time. For this reason, it was difficult to measure thephotoluminescence quantum yield with a good degree of accuracy inexisting methods.

The present disclosure was contrived in order to solve the aboveproblem, and an object thereof is to provide a spectrometry device and aspectrometry method that make it possible to measure thephotoluminescence quantum yield of a long afterglow emission materialwith a good degree of accuracy.

Solution to Problem

According to an aspect of the present disclosure, there is provided aspectrometry device configured to irradiate a long afterglow emissionmaterial with excitation light and measure a photoluminescence quantumyield, the device including: a light source configured to output theexcitation light; an integrator configured to have an internal space inwhich the long afterglow emission material is disposed, and output lightfrom the internal space as detection light; a spectroscopic detectorconfigured to spectroscopically disperse the detection light and acquirespectral data; an analysis unit configured to analyze thephotoluminescence quantum yield of the long afterglow emission materialon the basis of the spectral data; and a control unit configured tocontrol switching between presence and absence of input of theexcitation light to the internal space and an exposure time of thedetection light in the spectroscopic detector, wherein the control unitcontrols the light source so that the input of the excitation light tothe internal space is maintained in a first period in which theacquisition of the spectral data through the spectroscopic detector isstarted, and that the input of the excitation light to the internalspace is stopped in a second period subsequent to the first period, andcontrols the spectroscopic detector so that an exposure time of thedetection light in the second period becomes longer than an exposuretime of the detection light in the first period.

In this spectrometry device, the excitation light is continuously inputto the long afterglow emission material within the integrator in thefirst period in which the acquisition of the spectral data is started.The intensity of the excitation light is extremely higher than theintensity of light emission in the long afterglow emission material. Forthis reason, the exposure time of the detection light in the firstperiod is made shorter than the exposure time of the detection light inthe second period, whereby it is possible to prevent the saturation of asignal in the spectroscopic detector. In addition, in this spectrometrydevice, the input of the excitation light to the long afterglow emissionmaterial within the integrator is stopped in the second periodsubsequent to the first period, and the exposure time of the detectionlight in the second period is made longer than the exposure time of thedetection light in the first period. Thereby, light emission of the longafterglow emission material in which its intensity is extremely lowerthan the excitation light and the intensity fluctuates over time afterthe input of the excitation light is stopped can be detected with asufficient S/N ratio. Therefore, in this spectrometry device, it ispossible to measure the photoluminescence quantum yield of the longafterglow emission material with a good degree of accuracy. In addition,the exposure time of the detection light in the second period is madelonger than the exposure time of the detection light in the firstperiod, so that even in a case where the emission lifetime of the longafterglow emission material is long, it is possible to suppress anincrease in the amount of data required for the acquisition of spectraldata.

In addition, the control unit may control the spectroscopic detector sothat an exposure time of the detection light becomes longer after anelapse of a certain period of time from start of the second period. Inthis case, it is possible to more suitably suppress an increase in theamount of data required for the acquisition of the spectral data.

In addition, the spectroscopic detector may acquire a peak value of anintensity of the excitation light in the first period and a peak valueof an intensity of light emission in the long afterglow emissionmaterial on the basis of the spectral data, and the control unit maydetermine an exposure time of the detection light during start of thesecond period on the basis of a product of a ratio of the peak value ofthe intensity of the excitation light to the peak value of the intensityof light emission and the exposure time of the detection light in thefirst period. By using such a ratio, it is possible to optimize theexposure time of the detection light during the start of the secondperiod, and to prevent the saturation of a signal in the spectroscopicdetector in the second period.

In addition, the analysis unit may analyze a time profile of anintensity of light emission in the long afterglow emission material bystandardizing the intensity of light emission in the long afterglowemission material in the first period on the basis of the exposure timeof the detection light in the first period, and standardizing theintensity of light emission in the long afterglow emission material inthe second period on the basis of the exposure time of the detectionlight in the second period. Thereby, even in a case where the exposuretime is dynamically changed during a measurement period, it is possibleto analyze the time profile of the intensity of light emission in thelong afterglow emission material with a good degree of accuracy.

In addition, the integrator may be an integration hemisphere. Even in acase where an integration hemisphere is used as the integrator, it ispossible to measure the photoluminescence quantum yield of the longafterglow emission material with a good degree of accuracy.

According to an aspect of the present disclosure, there is provided aspectrometry method of irradiating a long afterglow emission materialwith excitation light and measuring a photoluminescence quantum yield,the method including: a spectral data acquisition step ofspectroscopically dispersing detection light, output from an integratorhaving an internal space in which the long afterglow emission materialis disposed, through a spectroscopic detector and acquiring spectraldata; and a photoluminescence quantum yield analysis step of analyzingthe photoluminescence quantum yield of the long afterglow emissionmaterial on the basis of the spectral data, wherein, in the spectraldata acquisition step, input of the excitation light to the internalspace is maintained in a first period in which the acquisition of thespectral data through the spectroscopic detector is started, and theinput of the excitation light to the internal space is stopped in asecond period subsequent to the first period, and an exposure time ofthe detection light in the second period in the spectroscopic detectoris made longer than an exposure time of the detection light in the firstperiod.

In this spectrometry method, the excitation light is continuously inputto the long afterglow emission material within the integrator in thefirst period in which the acquisition of the spectral data is started.The intensity of the excitation light is extremely higher than theintensity of light emission in the long afterglow emission material. Forthis reason, the exposure time of the detection light in the firstperiod is made shorter than the exposure time of the detection light inthe second period, whereby it is possible to prevent the saturation of asignal in the spectroscopic detector. In addition, in this spectrometrydevice, the input of the excitation light to the long afterglow emissionmaterial within the integrator is stopped in the second periodsubsequent to the first period, and the exposure time of the detectionlight in the second period is made longer than the exposure time of thedetection light in the first period. Thereby, light emission of the longafterglow emission material in which its intensity is extremely lowerthan the excitation light and the intensity fluctuates over time afterthe input of the excitation light is stopped can be detected with asufficient S/N ratio. Therefore, in this spectrometry method, it ispossible to measure the photoluminescence quantum yield of the longafterglow emission material with a good degree of accuracy. The exposuretime of the detection light in the second period is made longer than theexposure time of the detection light in the first period, so that evenin a case where the emission lifetime of the long afterglow emissionmaterial is long, it is possible to suppress an increase in the amountof data required for the acquisition of spectral data.

In addition, in the spectral data acquisition step, an exposure time ofthe detection light in the spectroscopic detector may be made longerafter an elapse of a certain period of time from start of the secondperiod. In this case, it is possible to more suitably suppress anincrease in the amount of data required for the acquisition of thespectral data.

In addition, the spectrometry method may further include a peakacquisition step of acquiring a peak value of an intensity of theexcitation light in the first period and a peak value of an intensity oflight emission in the long afterglow emission material on the basis ofthe spectral data, and in the spectral data acquisition step, anexposure time of the detection light during start of the second periodmay be determined on the basis of a product of a ratio of the peak valueof the intensity of the excitation light to the peak value of theintensity of light emission and the exposure time of the detection lightin the first period. By using such a ratio, it is possible to optimizethe exposure time of the detection light during the start of the secondperiod, and to prevent the saturation of a signal in the spectroscopicdetector in the second period.

In addition, in the photoluminescence quantum yield analysis step, atime profile of an intensity of light emission in the long afterglowemission material may be analyzed by standardizing the intensity oflight emission in the long afterglow emission material in the firstperiod on the basis of the exposure time of the detection light in thefirst period, and standardizing the intensity of light emission in thelong afterglow emission material in the second period on the basis ofthe exposure time of the detection light in the second period. Thereby,even in a case where the exposure time is dynamically changed during ameasurement period, it is possible to analyze the time profile of theintensity of light emission in the long afterglow emission material witha good degree of accuracy.

In addition, an integration hemisphere may be used as the integrator.Even in a case where an integration hemisphere is used as theintegrator, it is possible to measure the photoluminescence quantumyield of the long afterglow emission material with a good degree ofaccuracy.

Advantageous Effects of Invention

According to the present disclosure, it is possible to measure thephotoluminescence quantum yield of a long afterglow emission materialwith a good degree of accuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an embodiment of aspectrometry device.

FIG. 2 is a diagram illustrating a principle of calculation of aphotoluminescence quantum yield.

FIG. 3 is a diagram illustrating a temporal variation in the intensityof light emission in a long afterglow emission material.

FIG. 4 is a diagram illustrating an example of a time profile of theintensity of light emission in the long afterglow emission material andcontrol of exposure times of detection light.

FIG. 5 is a diagram illustrating an example of calculation of the numberof absorbed photons of the long afterglow emission material.

FIG. 6 is a diagram illustrating an example of calculation of the numberof light emission photons in the long afterglow emission material.

FIG. 7 is a schematic diagram illustrating another embodiment of thespectrometry device.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment of a spectrometry device and aspectrometry method according to an aspect of the present disclosurewill be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating an embodiment of aspectrometry device. As shown in the drawing, a spectrometry device 1includes a light source 2, an integrator 3, a spectroscopic detector 4,and a computer 5. This spectrometry device 1 is configured as a devicethat measures the photoluminescence quantum yield of a light-emittingmaterial. The light-emitting material which is an object to be measuredis a long afterglow emission material such as a luminescent material ora phosphorescent material. The long afterglow emission material is, forexample, a material that accumulates sunlight or excitation light of afluorescent lamp or the like, and sustains light emission for a constantperiod of time even after radiation of the excitation light is stopped.Examples of the long afterglow emission material include an inorganicmaterial or an organic material containing a rare metal, and the like.The form of the long afterglow emission material can variously be asolution, a thin film, a powder, or the like.

The light source 2 is a device that outputs excitation light. Theexcitation light which is output from the light source 2 is light havinga wavelength that excites a long afterglow emission material andexpresses light emission. The light source 2 is, for example, amonochrome light source having a monochromator attached to a xenon lamp.The light source 2 may be constituted by a laser diode that outputs alaser beam having a wavelength corresponding to the absorptionwavelength of a long afterglow emission material. The light source 2 maybe a wavelength variable light source. The light source 2 may include anND filter, a relay optical system, a shutter, or the like. The lightsource 2 may be configured to be capable of outputting standard lightfor performing calibration of the sensitivity of the entire device.

The integrator 3 includes a main body 12 provided with an internal space11 in which a long afterglow emission material S is disposed, an inputunit 13 that inputs excitation light which is output from the lightsource 2 to the internal space 11, and an output unit 14 that outputslight from the internal space 11 to the outside. In the presentembodiment, the integrator 3 is an integrating sphere, and the main body12 and the internal space 11 are formed in a sphere shape. The sphericalportion of the inner wall of the main body 12 is formed as a wallsurface having high reflectance and excellent diffusibility, and itsplanar portion is formed as a flat mirror having high reflectance.

The main body 12 is provided with a sample attachment portion 15. Aholding container for holding the long afterglow emission material S isattached to the sample attachment portion 15. For example, in a casewhere the long afterglow emission material S is a liquid, a cell for asolution sample formed of a transparent material (such as, for example,silica glass or plastic) that transmits light, or the like is attachedto the sample attachment portion 15 as a sample container. In addition,in a case where the long afterglow emission material S is a solid suchas a powder or a thin film, a cell for a solid sample formed of atransparent material (such as, for example, silica glass or plastic)that transmits light or a metal, or the like is attached to the sampleattachment portion 15 as a sample container.

Meanwhile, the long afterglow emission material S may not necessarily becompletely disposed within the internal space 11 of the integrator 3, ora portion of the long afterglow emission material S may be disposed inthe internal space 11 of the integrator 3. For example, using an opticalattachment attached to the sample attachment portion 15, a sampledisposed outside the inner wall of the integrator 3 may be opticallydisposed in the internal space 11 of the integrator 3.

The input unit 13 inputs excitation light to the internal space 11. Theinput unit 13 is optically connected to the light source 2 through alight guide for input 16. As the light guide for input 16, for example,an optical fiber or the like can be used. In addition, the output unit14 outputs light from the internal space 11. The output unit 14 isoptically connected to the spectroscopic detector 4 through a lightguide for output 17. As the light guide for output 17, for example, anoptical fiber or the like can be used.

In the integrator 3, the excitation light from the light source 2 isinput from the input unit 13 to the internal space 11, and theexcitation light is reflected within the internal space 11 in amultiplex diffusion manner. In addition, in the integrator 3, lightemitted by the excitation light being radiated to the long afterglowemission material S is reflected within the internal space 11 in amultiplex diffusion manner. The excitation light and the emitted lightreflected within the internal space 11 in a multiplex diffusion mannerare input, as detection light, from the output unit 14 to thespectroscopic detector 4.

The spectroscopic detector 4 spectroscopically disperses detection lightwhich is output from the integrator 3, and acquires spectral data. Thespectroscopic detector 4 spectroscopically disperses the detection lightinto individual wavelength components using a spectroscopic element suchas, for example, a grating or a prism, and detects the intensity of thespectroscopically dispersed light of each wavelength using an opticalsensor group. The optical sensor group is configured by, for example, aplurality of light receiving units being arranged one-dimensionally. Theoptical sensor group detects the intensity of light having eachwavelength component using a light receiving unit corresponding to eachwavelength, and acquires spectral data of the excitation light and theemitted light. The spectroscopic detector 4 outputs the acquiredspectral data to the computer 5.

Examples of an optical sensor of the spectroscopic detector 4 to be usedinclude a CCD linear image sensor and a CMOS linear image sensor formedon a silicon substrate. These sensors are sensitive to light having, forexample, a wavelength of 360 nm to 1,100 nm. In addition, examples ofthe optical sensor of the spectroscopic detector 4 include an InGaAslinear image sensor. This sensor is sensitive to light having, forexample, a wavelength of 900 nm to 1,650 nm. The spectroscopic detector4 can make the exposure time of the detection light set variable, andchanges the exposure time during measurement on the basis ofpredetermined conditions (which will be described later).

The computer 5 is configured to include a memory such as, for example, aRAM or a ROM, a processor (an arithmetic circuit) such as a CPU, acommunication interface, and a storage unit such as a hard disk.Examples of such a computer 5 include a personal computer, amicrocomputer, a cloud server, a smart device (such as a smartphone or atablet terminal), and the like. In addition, the computer 5 includes adisplay unit 18 such as a monitor, a keyboard, and an input unit 19 suchas a mouse.

The computer 5 functions as an analysis unit 21 and a control unit 22 byexecuting a program stored in a memory in a CPU of a computer system.The analysis unit 21 analyzes the photoluminescence quantum yield of thelong afterglow emission material S on the basis of the spectral data ofthe excitation light and the emitted light acquired by the spectroscopicdetector 4. The control unit 22 executes control of the light source 2and the spectroscopic detector 4. The control unit 22 controls anoperation of the light source 2, and performs switching between thepresence and absence of input of the excitation light to the internalspace 11. In addition, the control unit 22 controls the spectroscopicdetector 4, and controls the exposure time of the detection light in thespectroscopic detector 4. The details of control will be describedlater.

Next, a method of measuring a photoluminescence quantum yield of thelong afterglow emission material S using the above-described thespectrometry device 1 will be described.

In this measuring method, the reference measurement and the samplemeasurement described above are performed. The sample measurement isconfigured to include a spectral data acquisition step (step S01) and aphotoluminescence quantum yield analysis step (step S02). The spectraldata acquisition step is a step of spectroscopically dispersingdetection light, output from the integrator 3 having the internal space11 in which the long afterglow emission material S is disposed, throughthe spectroscopic detector 4 and acquiring spectral data. Thephotoluminescence quantum yield analysis step is a step of analyzing thephotoluminescence quantum yield of the long afterglow emission materialS on the basis of the spectral data.

The photoluminescence quantum yield is one evaluation item of alight-emitting material, and is a value indicating the light emissionefficiency of the light-emitting material. Generally, in a case whereexcitation light is absorbed into a light-emitting material, lightemission such as fluorescence or phosphorescence and heat dissipationcaused by no radiation transition are performed. A photoluminescencequantum yield Φ_(PL) indicates the degree of this light emission, and iscalculated by dividing the number of photons N_(L) emitted from alight-emitting material by the number of photons N_(A) absorbed into thelight-emitting material.

FIG. 2 is a diagram illustrating a principle of calculation of aphotoluminescence quantum yield. In the drawing, the horizontal axisrepresents a wavelength, the vertical axis represents an intensity, anda spectrum S1 during the reference measurement and a spectrum S2 duringthe sample measurement are plotted. The reference measurement is a stepof acquiring spectral data of detection light without disposing the longafterglow emission material S in the internal space 11 of the integrator3. In the reference measurement, excitation light is continuously inputto the integrator 3 during the measurement. The spectrum S1 which isobtained in the reference measurement corresponds to the spectral dataof the excitation light which is output from the light source 2.

The sample measurement is a step of disposing the long afterglowemission material S in the internal space 11 of the integrator 3 andacquiring the spectral data of detection light. In the samplemeasurement, the excitation light is input to the integrator 3 over aconstant period of time from the start of the measurement, and output ofthe excitation light is stopped after an elapse of a certain period oftime. Thereafter, the measurement is ended at a point in time when lightemission of the long afterglow emission material S exceeds a thresholdand attenuates.

A spectrum S1 _(a) appearing on a short wavelength side (here,approximately 300 nm to 400 nm) in the spectrum S1 which is obtained inthe reference measurement is equivalent to a component of the excitationlight. A spectrum S1 _(b) appearing at a wavelength region (here,approximately 480 nm to 650 nm) different from the spectrum S1 _(a) inthe spectrum S1 which is obtained in the reference measurement isequivalent to a component of the excitation light (or background light)in the detection light. A spectrum S2 _(a) appearing at a wavelengthregion corresponding to the spectrum S1 _(a) in the spectrum S2 which isobtained in the sample measurement corresponds to spectral data of thecomponent of the excitation light in the detection light. A spectrum S2_(b) appearing at a wavelength region corresponding to the spectrum S1_(b) in the spectrum S2 which is obtained in the sample measurementcorresponds to spectral data of a component of emitted light in thedetection light. Therefore, the number of photons N_(A) absorbed intothe light-emitting material is calculated on the basis of a region R1obtained by deducting the spectrum S2 _(a) from the spectrum S1 _(a),and the number of photons N_(L) emitted from the light-emitting materialis calculated on the basis of a region R2 obtained by deducting thespectrum S1 _(b) from the spectrum S2 _(b).

In a case where the long afterglow emission material S is a measurementtarget, there is a problem in that the intensity of light emission inthe long afterglow emission material S is extremely (approximately onefigure) weaker than the intensity of the excitation light, and that theintensity of light emission after the radiation of the excitation lightis stopped fluctuates over time. For example, FIG. 3 is a diagram inwhich the spectrum S1 obtained in the reference measurement and aplurality of spectra S2 obtained by performing the sample measurementmultiple times at constant time intervals are plotted. In the case of anormal light-emitting material, there is little fluctuation in a portionequivalent to the spectrum S2 _(b) even in a case where the samplemeasurement is performed multiple times, but in the result of FIG. 3 forthe long afterglow emission material S, the number of photons indicatedby the spectrum S2 _(b) increases whenever the sample measurement isperformed. Therefore, it can be understood that the photoluminescencequantum yield of the long afterglow emission material S in this casegradually increases over time.

In measuring the photoluminescence quantum yield of such a longafterglow emission material S, in a measurement method of the relatedart, the exposure time of the detection light in the spectroscopicdetector is set to be constant throughout the entire period from thestart of measurement to the end of measurement. This exposure time isset to a short time of, for example, approximately several tens of msecin order to avoid the saturation of a signal in the spectroscopicdetector due to the excitation light. However, when the detection lightis detected at the same exposure time even after output of theexcitation light is stopped, there may be a problem in that the S/Nratio of detection to light emission of the long afterglow emissionmaterial S decreases, and the accuracy of measurement of thephotoluminescence quantum yield is not sufficiently obtained.

On the other hand, in the measurement method using the spectrometrydevice 1 according to the present embodiment, control of switchingbetween turning on and turning off of the light source 2 by the controlunit 22 and control of the exposure time of detection light in thespectroscopic detector 4 are executed in the spectral data acquisitionstep. FIG. 4 is a diagram illustrating an example of a time profile ofthe intensity of light emission in the long afterglow emission materialand control of exposure times of the detection light. In the spectraldata acquisition step, as shown in FIG. 4 , a first period T₁ is startedwith the start of output of the excitation light by the light source 2,and the acquisition of spectral data of the detection light in thespectroscopic detector 4 is started. During the first period T₁, inputof the excitation light to the internal space 11 is maintained, and theexcitation light continues to be radiated to the long afterglow emissionmaterial S. Thereby, the long afterglow emission material S is excited,and light emission is started. In the first period T₁, light emission ofthe long afterglow emission material S increases and then converges on aconstant peak intensity. In addition, the exposure time of the detectionlight in the spectroscopic detector 4 is set to a shortest exposure timet₁ throughout the entire measurement period so that saturation of asignal in the spectroscopic detector 4 does not occur. In the example ofFIG. 4 , the exposure time t₁ is set to, for example, 20 msec.

In a second period T₂ subsequent to the first period T₁, output of theexcitation light by the light source 2 is stopped. In the second periodT₂, the incidence of the excitation light on the long afterglow emissionmaterial S is stopped, but light emission of the long afterglow emissionmaterial S in which the excitation light is accumulated is sustained fora constant period of time while gradually attenuating. The timing of thestart of the second period T₂ is determined on the basis of, forexample, the peak value of the intensity of light emission. In thiscase, the intensity of light emission during the first period T₁ ismonitored by the spectroscopic detector 4, and output of the excitationlight from the light source 2 is stopped in a case where a fluctuationper unit time in the peak value of the intensity of light emission isset to be equal to or less than a threshold (for example, 1%).

In addition, in the second period T₂, the exposure time of the detectionlight in the spectroscopic detector 4 is set to an exposure time t₂longer than the exposure time t₁ in the first period T₁. The exposuretime t₂ may be determined by integrating any constant with the exposuretime t₁. In addition, the exposure time t₂ may be determined using theratio of the peak value of the intensity of the excitation light to thepeak value of the intensity of light emission. In this case, the peakvalue of the intensity of the excitation light and the peak value of theintensity of light emission during the first period T₁ are monitored bythe spectroscopic detector 4 (peak acquisition step), a ratio iscalculated by dividing the peak value of the intensity of the excitationlight by the peak value of the intensity of light emission. The exposuretime t₂ is determined by integrating the calculated ratio with theexposure time t₁. For example, in a case where the exposure time t₁ is20 msec, and the ratio is 10, the exposure time t₂ is set to 200 msec.When the ratio is calculated, it is preferable that a value after theintensity is stabilized is used as the peak value of the intensity oflight emission.

The exposure time t₂ of the detection light in the second period T₂ maybe maintained until the end of measurement, but the spectroscopicdetector 4 may be controlled so that the exposure time of the detectionlight becomes longer after an elapse of a certain period of time fromthe start of the second period T₂. In this case, for example, when thethreshold of the intensity of light emission is set in advance, and theintensity of light emission in the second period T₂ attenuates and isset to be equal to or less than the threshold, the exposure time of thedetection light is set to an exposure time t₃ longer than the exposuretime t₂. There is no particular limitation to the value of the exposuretime t₃, but the exposure time t₃ may be determined by integrating, forexample, the exposure time t₂ with any coefficient. For example, in acase where the exposure time t₂ is 200 msec, and the coefficient is 10,the exposure time t₂ is set to 2,000 msec.

In addition, in the photoluminescence quantum yield analysis step, inanalyzing the time profile of the intensity of light emission in thelong afterglow emission material S, the intensity of light emission inthe long afterglow emission material S in the first period T₁ isstandardized on the basis of the exposure time t₁ of the detection lightin the first period T₁. In addition, the intensity of light emission inthe long afterglow emission material S in the second period T₂ isstandardized on the basis of the exposure time t₂ of the detection lightin the second period T₂. In a case where the exposure period is set fromthe exposure time t₂ to the exposure time t₃ after an elapse of acertain period of time in the second period T₂, a period after the settime is standardized on the basis of the exposure time t₃.

Meanwhile, in the photoluminescence quantum yield analysis step, incalculating the photoluminescence quantum yield of the long afterglowemission material S on the basis of the time profile of the intensity oflight emission in the long afterglow emission material S, the number ofabsorbed photons of the long afterglow emission material S may beobtained on the basis of excitation light spectral data in the firstperiod T₁. In this case, regarding the calculation of the number ofabsorbed photons, specifically, an extraction window (A-B in FIG. 3 ) isfirst set with respect to the spectrum S1 during the referencemeasurement and the spectrum S2 during the sample measurement which arerepresented by the wavelength axis, and as shown in FIG. 5 , excitationlight spectral data L1 during the reference measurement and excitationlight spectral data L2 during the sample measurement are acquired withrespect to the time axis. Next, the integrated value of the number ofphotons of the excitation light spectral data L2 in the first period T₁is subtracted from the integrated value of the number of photons of theexcitation light spectral data L1 in the first period T₁, and the numberof absorbed photons of the long afterglow emission material S isobtained.

In addition, in the photoluminescence quantum yield analysis step, incalculating the photoluminescence quantum yield of the long afterglowemission material S on the basis of the time profile of the intensity oflight emission in the long afterglow emission material S, the number oflight emission photons of the long afterglow emission material S may beobtained on the basis of light emission spectral data in any of 1) thefirst period T₁, 2) the second period T₂, and 3) a total period T₁₊₂ ofthe first period T₁ and the second period T₂. In this case, regardingthe calculation of the number of light emission photons, specifically,an extraction window (C-D in FIG. 3 ) is first set with respect to thespectrum S2 during the sample measurement represented by the wavelengthaxis. As shown in FIG. 6 , the number of light emission photons isobtained by light emission spectral data L3 which is obtained bysubtracting the number of photons of the excitation light (referencemeasurement result) from light emission photons (sample measurementresult) in the extraction window C-D. Finally, the photoluminescencequantum yield of the long afterglow emission material S is calculated bydividing the number of light emission photons by the number of absorbedphotons.

As described above, in the spectrometry device 1, the excitation lightis continuously input to the long afterglow emission material S withinthe integrator 3 in the first period T₁ in which the acquisition ofspectral data is started. The intensity of the excitation light isextremely higher than the intensity of light emission in the longafterglow emission material S. For this reason, the exposure time t₁ ofthe detection light in the first period T₁ is made shorter than theexposure time t₂ of the detection light in the second period T₂, wherebyit is possible to prevent the saturation of a signal in thespectroscopic detector 4. In addition, in the spectrometry device 1, theinput of the excitation light to the long afterglow emission material Swithin the integrator 3 is stopped in the second period T₂ subsequent tothe first period T₁, and the exposure time t₂ of the detection light inthe second period T₂ is made longer than the exposure time t₁ of thedetection light in the first period T₁. Thereby, light emission of thelong afterglow emission material S in which its intensity is extremelylower than the excitation light and the intensity fluctuates over timeafter the input of the excitation light is stopped can be detected witha sufficient S/N ratio. Therefore, in the spectrometry device 1, it ispossible to measure the photoluminescence quantum yield of the longafterglow emission material S with a good degree of accuracy. Inaddition, the exposure time t₂ is made longer than the exposure time t₁,so that even in a case where the emission lifetime of the long afterglowemission material is long, it is possible to suppress an increase in theamount of data required for the acquisition of spectral data.

In addition, in the spectrometry device 1, the control unit 22 cancontrol the spectroscopic detector 4 so that the exposure time of thedetection light becomes longer after an elapse of a certain period oftime from the start of the second period T₂. Thereby, it is possible tomore suitably suppress an increase in the amount of data required forthe acquisition of spectral data.

In addition, in the spectrometry device 1, the spectroscopic detector 4acquires the peak value of the intensity of the excitation light in thefirst period T₁ and the peak value of the intensity of light emission inthe long afterglow emission material S on the basis of the spectraldata, and the control unit 22 determines the exposure time t₂ of thedetection light during the start of the second period T₂ on the basis ofthe product of the ratio of the peak value of the intensity of theexcitation light to the peak value of the intensity of light emissionand the exposure time t₁ of the detection light in the first period T₁.By using such a ratio, it is possible to optimize the exposure time t₂of the detection light during the start of the second period T₂, and toprevent the saturation of a signal in the spectroscopic detector 4 inthe second period T₂.

In addition, in the spectrometry device 1, the analysis unit 21 analyzesthe time profile of the intensity of light emission in the longafterglow emission material S by standardizing the intensity of lightemission in the long afterglow emission material in the first period T₁on the basis of the exposure time t₁ of the detection light in the firstperiod T₁, and standardizing the intensity of light emission in the longafterglow emission material in the second period T₂ on the basis of theexposure time t₂ of the detection light in the second period T₂.Thereby, even in a case where the exposure time is dynamically changedduring a measurement period, it is possible to analyze the time profileof the intensity of light emission in the long afterglow emissionmaterial S with a good degree of accuracy.

Meanwhile, in the above embodiment, the integrator 3 constituted by anintegrating sphere is used as shown in FIG. 1 , but an integrator 30constituted by an integration hemisphere may be used as shown in FIG. 7. A main body 32 and an internal space 31 of this integrator 30 areformed in a hemisphere shape. The spherical portion of the inner wall ofthe main body 12 is formed as a wall surface having high reflectance andexcellent diffusibility, and its planar portion is formed as a flatmirror having high reflectance. An input unit 33 and an output unit 34may be provided at any position of the spherical portion and the planarportion. Even in a case where an integration hemisphere is used as theintegrator 30 in this manner, it is possible to measure thephotoluminescence quantum yield of the long afterglow emission materialS with a good degree of accuracy.

REFERENCE SIGNS LIST

-   -   1 Spectrometry device,    -   2 Light source,    -   3, 30 Integrator,    -   4 Spectroscopic detector,    -   11 Internal space,    -   21 Analysis unit,    -   22 Control unit,    -   S Long afterglow emission material,    -   T₁ First period,    -   T₂ Second period,    -   t₁ Exposure time in first period,    -   t₂ Exposure time in second period

The invention claimed is:
 1. A spectrometry device configured toirradiate a long afterglow emission material with excitation light andmeasure a photoluminescence quantum yield, the device comprising: alight source configured to output the excitation light; an integratorconfigured to have an internal space in which the long afterglowemission material is disposed, and output light from the internal spaceas detection light; a spectroscopic detector configured tospectroscopically disperse the detection light and acquire spectraldata; an analyzer configured to analyze the photoluminescence quantumyield of the long afterglow emission material on the basis of thespectral data; and a controller configured to control switching betweenpresence and absence of input of the excitation light to the internalspace and an exposure time of the detection light in the spectroscopicdetector, wherein the controller controls the light source so that theinput of the excitation light to the internal space is maintained in afirst period in which the acquisition of the spectral data through thespectroscopic detector is started, and that the input of the excitationlight to the internal space is stopped in a second period subsequent tothe first period, and controls the spectroscopic detector so that anexposure time of the detection light in the second period becomes longerthan an exposure time of the detection light in the first period,wherein the detection light and the spectral data contain a componenthaving a longer wavelength than the excitation light, wherein the firstperiod is one during which input of the excitation light into theinternal space is maintained, and the second period is one during whichinput of the excitation light into the internal space is stopped,wherein the start timing of the second period is determined based on thefluctuation per unit time of a peak value of intensity of lightemission, wherein the spectroscopic detector acquires a peak value of anintensity of the excitation light in the first period and the peak valueof the intensity of light emission in the long afterglow emissionmaterial on the basis of the spectral data, and the controllerdetermines an exposure time of the detection light during start of thesecond period on the basis of a product of a ratio of the peak value ofthe intensity of the excitation light to the peak value of the intensityof light emission and the exposure time of the detection light in thefirst period.
 2. A spectrometry method of irradiating a long afterglowemission material with excitation light and measuring aphotoluminescence quantum yield, the method comprising: acquiringspectroscopically dispersing detection light, output from a n integratorhaving an internal space in which the long afterglow emission materialis disposed, through a spectroscopic detector and acquiring spectraldata; and analyzing the photoluminescence quantum yield of the longafterglow emission material on the basis of the spectral data, wherein,in the acquiring, input of the excitation light to the internal space ismaintained in a first period in which the acquisition of the spectraldata through the spectroscopic detector is started, and the input of theexcitation light to the internal space is stopped in a second periodsubsequent to the first period, and an exposure time of the detectionlight in the second period in the spectroscopic detector is made longerthan an exposure time of the detection light in the first period,wherein the detection light and the spectral data contain a componenthaving a longer wavelength than the excitation light, wherein the firstperiod is one during which input of the excitation light into theinternal space is maintained, and the second period is one during whichinput of the excitation light into the internal space is stopped, andwherein the start timing of the second period is determined based on thefluctuation per unit time of a peak value of intensity of lightemission, further comprising acquiring a peak value of an intensity ofthe excitation light in the first period and the peak value of theintensity of light emission in the long afterglow emission material onthe basis of the spectral data, wherein, in the peak acquiring, anexposure time of the detection light during start of the second periodis determined on the basis of a product of a ratio of the peak value ofthe intensity of the excitation light to the peak value of the intensityof light emission and the exposure time of the detection light in thefirst period.